Sorbent composition for use in a flue gas train including a baghouse

ABSTRACT

A sorbent composition for enhanced baghouse function is described. The composition may include a sorbent such as powder activated carbon as well as an additive that is a heat moderator or a permeability agent. The heat moderator may act as a heat sink or barrier. Heat moderators may include in non-limiting examples phyllosilicates, cyclosilicates, or nesosilicates that may include, montmorillonite, bentonite, halloysite, aluminum silicates, muscovite, illite, kaolin, andalusite, kyanite, sillimanite, metakaolin, mullite, polymers, such as chitosan, and/or clays, either natural or synthetic (e.g., montmorillonite), or polyethylenimine. Permeability may be affected by mixing sorbents of lower D50 with sorbents of higher D50 in various ratios, or addition of a permeability agent such as a phyllosilicate, perlite, silica, diatomaceous earth. Further, a permeability agent such as a fluoropolymer may be coated onto or admixed with the sorbent. Diatomaceous earth, perlites, or silicates may also increase permeability. The compositions are particularly useful in flue gas treatment systems with baghouse separation units in that they have reduced combustibility and increased permeability properties.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of U.S. Provisional PatentApplication No. 62/086,292 filed on Dec. 2, 2014, entitled “SORBENTCOMPOSITION FOR USE IN A FLUE GAS TRAIN INCLUDING A BAGHOUSE,” which isincorporated herein by reference in its entirety.

FIELD

This disclosure relates to the field of sorbent compositions thatimprove the performance of baghouse units of flue gas stream airpollution control systems.

BACKGROUND

A baghouse (“BH”) unit, also called a fabric filter unit, is used as anair pollution control device and functions to capture particulate matterfrom flue gas streams of coal-fired electricity generating plants orwaste-burning industrial boilers. Particulate matter in flue gas streamsmay include fly ash from the boiler, sorbents and other conditioningagents added to capture contaminants in the stream such as mercury,hydrochloric acid (HCl), bromine, and others. BH units are highlyefficient particulate collection devices, operating effectively in abroad range of incoming loading or particle size. Further, BH units mayserve as dry collection devices for removing contaminant gases and heavymetals via increased exposure to adsorbents. Recently many sites havebegun to use the TOXECON™ system that utilizes both an electrostaticprecipitator (“ESP”) and BH unit. In this system, a sorbent, used tocapture especially mercury, is injected downstream from the ESP unitsuch that fly ash can be collected in the ESP and sold to concreteproducers. BH units in these systems serve to capture remainingparticulate matter, sorbent, and contaminants from the flue gas streamprior to emission from the stack serving as the last emission controldevice. The TOXECON™ system is described in U.S. Pat. No. 5,505,766 byChang, which is incorporated herein by reference in its entirety.

In the United States and Canada, federal and state/provincialregulations have been implemented or are being considered to reducemercury emissions, particularly from coal-fired power plants, steelmills, cement kilns, waste incinerators and boilers, industrialcoal-fired boilers, and other coal-combusting facilities. For example,the United States Environmental Protection Agency (U.S. EPA) haspromulgated Mercury Air Toxics Standards (MATS), which would among otherthings require coal-fired power plants to capture at least approximately80% to 90% of their mercury emissions. The rule applies to fourpollutant classes: mercury (Hg), acid gasses such as sulfur dioxide(SO₂) and hydrochloric acid (HCl), filterable particulate matter (fPM),and non-mercury metals.

The leading sorbent for mercury control from coal-fired power plants isactivated carbon. Activated carbon, particularly powder activated carbon(“PAC”), can be injected into the flue gas emitted by the boiler of apower plant. PAC is a porous carbonaceous material having a high surfacearea, which exposes significant amounts of beneficial chemicallyfunctional and reaction sites and which creates high adsorptivepotential for many compounds, including capturing mercury from the fluegas.

SUMMARY

In one embodiment, a sorbent composition that enhances baghouse unitperformance is disclosed. The sorbent composition includes a sorbenthaving a median particle diameter (D50) of not greater than about 30 μm,and at least a first heat moderator.

A number of characterizations, refinements, enhancements and additionalfeatures are applicable to this embodiment of a sorbent composition thatenhances baghouse unit performance. These characterizations,refinements, enhancements and additional features are applicable to thisembodiment of a sorbent composition individually or in any combination.

In one characterization of the sorbent composition that enhancesbaghouse unit performance, the first heat moderator is selected from thegroup consisting of phyllosilicates, cyclosilicates, nesosilicates,colloidal silicates, aluminum silicates, mullite, perlite,organo-halogens, organo-phosphates, sodium sulfite, organicphosphinates, and combinations thereof.

In one particular example, the first heat moderator comprises aphyllosilicate. In one characterization of this example, thephyllosilicate is selected from the group consisting of kaolin,montmorillonite, illite, vermiculite, muscovite, kyanite, sillimanite,metakaolin, aluminum phyllosilicates, and combinations thereof. In oneexemplary composition, the phyllosilicate comprises a montmorillonite(e.g., natural or synthetic montmorillonite).

In another example, the first heat moderator comprises an aluminumsilicate. In one characterization, the aluminum silicate is selectedfrom the group consisting of zeolites, halloysite, andalusite, kyanite,sillimanite, kaolin, metakaolin, mullite, feldspar group minerals, andcombinations thereof. In one particular form, the aluminum silicatecomprises halloysite. In another particular form, the aluminum silicatecomprises andalusite.

In another example, the first heat moderator comprises an aluminumphyllosilicate. In one characterization, the aluminum phyllosilicatecomprises bentonite.

In another example, the first heat moderator comprises a nesosilicate.In another example, the heat moderator comprises an organic phosphinate.In yet another example, the heat moderator comprises sodium sulfite.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the sorbent composition further comprises abinding agent. In one example of this embodiment, the binding agentcomprises a polymer that forms a charged species in water. In onecharacterization, the polymer that forms a charged species in watercomprises a polysaccharide. In one particular characterization, thepolysaccharide is selected from the group consisting of chitosan,dextran, cyclodextrin and cellulose. In another characterization, thepolymer that forms a charged species in water is selected from the groupconsisting of polyamines, polyacrylates and polyacrylamides. In oneform, the polymer is a polyamine that is selected from the groupconsisting of poly aminoester, and polyethylenimine. In another form,the polymer is the polyacrylamide poly[2-(N,N-dimethylamino)ethylmethacrylate. In one example of the sorbent composition that furthercomprises a binding agent, the heat moderator is coated onto thesorbent. In another example of the sorbent composition that furthercomprises a binding agent, the heat moderator is coated onto the bindingagent.

In one example of a sorbent composition that further comprises a bindingagent, the first heat moderator is selected from the group consisting ofphyllosilicates, cyclosilicates, nesosilicates, colloidal silicates,aluminum silicates, mullite, perlite, organo-halogens,organo-phosphates, sodium sulfite, organic phosphinates, andcombinations thereof. In one characterization, a second heat moderatoris coated onto the first heat moderator, wherein the second heatmoderator is selected from the group consisting of phyllosilicates,cyclosilicates, nesosilicates, colloidal silicates, aluminum silicates,mullite, perlite, organo-halogens, organo-phosphates, sodium sulfite,organic phosphinates, and combinations thereof. In one form of thischaracterization of the sorbent composition, a third heat moderator iscoated onto the second heat moderator, wherein the third heat moderatoris selected from a group consisting of phyllosilicates, cyclosilicates,nesosilicates, colloidal silicates, aluminum silicates, mullite,perlite, organo-halogens, organo-phosphates, sodium sulfite, organicphosphinates, and combinations thereof. In some forms, a fourth layer ofa heat moderator is coated onto the third heat moderator, wherein thefourth heat moderator is selected from a group consisting ofphyllosilicates, cyclosilicates, nesosilicates, colloidal silicates,aluminum silicates, mullite, perlite, organo-halogens,organo-phosphates, sodium sulfite, organic phosphinates, andcombinations thereof.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the heat moderator is present in thecomposition at a concentration of at least about 0.5 wt. % and notgreater than about 20 wt. %. In another embodiment, the binding agent ispresent in the composition at a concentration of at least about 0.05 wt.% and not greater than about 10 wt. %.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the sorbent composition comprises anoxidizing agent. In one example, the oxidizing agent comprises aninorganic halogen salt. In one characterization of this example, theinorganic halogen salt is selected from the group consisting of alkalimetal compounds and alkaline earth metal compounds. In one form, thealkali metal compound or alkali earth metal compound is selected fromthe group consisting of calcium hypochlorite, calcium hypobromite,calcium hypoiodite, calcium chloride, calcium bromide, calcium iodide,magnesium chloride, magnesium bromide, magnesium iodide, sodiumchloride, sodium bromide, sodium iodide, potassium chloride, potassiumbromide, potassium iodide and combinations thereof.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the composition further comprises a catalyticphase metal wherein the catalytic phase metal is selected from the groupconsisting of Fe, Cu, Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn, Sn, Ti, Ce, andmixtures thereof.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the composition further comprises an acid gasagent, the acid gas agent comprising a trivalent or higher Group 3 toGroup 14 metal-containing compound selected from the group consisting ofa carbonate, an oxide, a hydroxide, an ionic salt precursor to ahydroxide and combinations thereof. In one example of thischaracterization, the acid gas agent comprises aluminum hydroxide.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the composition further comprises a flow aid,wherein the flow aid is selected from the group consisting of graphite,talc, mica and combinations thereof. In one example of thischaracterization, the flow aid comprises graphite.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the wt. % of the sorbent having a size ofless than 5 μm comprises not more than about 10 wt. % of the totalcomposition.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the composition further comprises apermeability additive, wherein the permeability additive is selectedfrom the group consisting of perlite, silica, diatomaceous earth,zeolites, and combinations thereof.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the sorbent has a median particle diameter ofnot greater than about 15 μm. In one example, the sorbent has a medianparticle diameter of not greater than about 12 μm.

In another characterization of the sorbent composition that enhancesbaghouse unit performance, the specific enthalpy of the composition isat least about 10% less than the specific enthalpy of a composition thatconsists essentially of the sorbent. In one example, the specificenthalpy of the sorbent composition is at least about 15% less than thespecific enthalpy of a composition that consists essentially of thesorbent. In another example, the specific enthalpy of the composition isat least about 20% less than the specific enthalpy of a composition thatconsists essentially of the sorbent.

In another embodiment, a composition that enhances baghouse unitperformance is disclosed, where the composition comprises a sorbenthaving a median particle diameter (D50) of not greater than about 30 μm,and comprises a permeability additive. In one characterization, thepermeability additive is selected from the group consisting of perlite,silica, diatomaceous earth, zeolite and combinations thereof.

In another embodiment, a composition that enhances baghouse unitperformance is disclosed, wherein the composition comprises a sorbenthaving a median particle diameter (D50) of not greater than about 30 μm,and comprises a surface agent.

A number of characterizations, refinements, enhancements and additionalfeatures are applicable to this embodiment of a sorbent composition thatenhances baghouse unit performance and comprises a surface agent. Thesecharacterizations, refinements, enhancements and additional features areapplicable to this embodiment of a sorbent composition individually orin any combination.

In one characterization, the surface agent comprises a fluoropolymer.According to one refinement of this characterization, the fluoropolymeris selected from the group consisting of polytetrafluoroethylene (PTFE),polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF),polychlorotrifluoroethene (PCTFE), perfluoroalkoxy alkane (PFA),fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene(ETFE), ethylene chloro trifluoroethylene (ECTFE), fluorocarbon[chlorofluortrifluoroethylenevinylidene fluoride] (FPM/FKM),perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA), andcombinations or derivatives thereof.

In another characterization, the composition further comprises anoxidizing agent. In one example, the oxidizing agent comprises aninorganic halogen salt. In one refinement of this example, the inorganichalogen salt is selected from the group consisting of alkali metalcompounds and alkaline earth metal compounds. In a further refinement,the alkali metal compound or alkaline earth metal compound is selectedfrom the group consisting of calcium hypochlorite, calcium hypobromite,calcium hypoiodite, calcium chloride, calcium bromide, calcium iodide,magnesium chloride, magnesium bromide, magnesium iodide, sodiumchloride, sodium bromide, sodium iodide, potassium chloride, potassiumbromide, potassium iodide and combinations thereof.

In another characterization of this embodiment of a composition thatenhances baghouse unit performance, the composition further comprises acatalytic phase metal wherein the catalytic phase metal is selected fromthe group consisting of Fe, Cu, Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn, Sn,Ti, Ce, and mixtures thereof. In yet another characterization of thisembodiment of a composition that enhances baghouse unit performance, thecomposition further comprises an acid gas agent, the acid gas agentcomprising a trivalent or higher Group 3 to Group 14 metal-containingcompound selected from the group consisting of a carbonate, an oxide, ahydroxide, an ionic salt precursor to a hydroxide and combinationsthereof. In one example, the acid gas agent comprises aluminumhydroxide.

In another characterization of this embodiment of a composition thatenhances baghouse unit performance, the composition further comprises aflow aid, wherein the flow aid is selected from the group consisting ofgraphite, talc, mica and combinations thereof. In one example, the flowaid comprises graphite.

In another characterization of this embodiment of a composition thatenhances baghouse unit performance, the wt. % of the sorbent having asize of less than 5 μm comprises not more than about 10 wt. % of thetotal composition. In yet another characterization of this embodiment ofa composition that enhances baghouse unit performance, the compositionfurther comprises a permeability additive, wherein the permeabilityadditive is selected from the group consisting of perlite, silica,diatomaceous earth, zeolites, and combinations thereof. In anothercharacterization of this embodiment of a composition that enhancesbaghouse unit performance, the composition further comprise a heatmoderator selected from the group consisting of phyllosilicates,cyclosilicates, nesosilicates, colloidal silicates, aluminum silicates,mullite, perlite, organo-halogens, organo-phosphates, sodium sulfite,organic phosphinates, and combinations thereof. In one example, thesorbent composition of this characterization further comprises a bindingagent, wherein the binding agent comprises a polymer that forms acharged species in water.

In another characterization of this embodiment of a composition thatenhances baghouse unit performance, the sorbent has a median particlediameter of not greater than about 15 μm. In one refinement, the sorbenthas a median particle diameter of not greater than about 12 μm.

In another embodiment of this disclosure, a composition that enhancesbaghouse unit performance is disclosed, wherein the composition is amixture of at least a first sorbent and a second sorbent, the firstsorbent having a median particle diameter of not greater than about 30μm and at least about 20 μm, and the second sorbent having a medianparticle diameter of not greater than about 20 μm and at least about 8μm, wherein the median particle diameter of the second sorbent is lessthan the median particle diameter of the first sorbent.

A number of characterizations, refinements, enhancements and additionalfeatures are applicable to this embodiment of a sorbent composition thatenhances baghouse unit performance and comprises a surface agent. Thesecharacterizations, refinements, enhancements and additional features areapplicable to this embodiment of a sorbent composition individually orin any combination.

In one characterization of this embodiment, the first sorbent and thesecond sorbent comprise substantially the same sorbent material. Inanother characterization, the difference in median particle diameterbetween the first sorbent and the second sorbent is at least about 5 μm.In one example of this characterization, the weight ratio of the firstsorbent to the second sorbent is not greater than about 5:1. In anotherexample, the weight ratio of the first sorbent to the second sorbent isnot greater than about 4:1. In another characterization, the weightratio of the first sorbent to the second sorbent is at least about 1:6.In yet another characterization, the weight ratio of the first sorbentto the second sorbent is at least about 1:1. In yet anothercharacterization, the weight ratio of the first sorbent to the secondsorbent is at least about 2:1.

In another characterization of this composition that enhances baghouseunit performance, the composition further comprises an oxidizing agent.In one example, the the oxidizing agent comprises an inorganic halogensalt. In a further refinement of this example, the inorganic halogensalt is selected from the group consisting of alkali metal compounds andalkaline earth metal compounds. In yet a further refinement, the alkalimetal compound or alkaline earth metal compound is selected from thegroup consisting of calcium hypochlorite, calcium hypobromite, calciumhypoiodite, calcium chloride, calcium bromide, calcium iodide, magnesiumchloride, magnesium bromide, magnesium iodide, sodium chloride, sodiumbromide, sodium iodide, potassium chloride, potassium bromide, potassiumiodide and combinations thereof.

In another characterization of this composition that enhances baghouseunit performance, the composition further comprises a catalytic phasemetal wherein the catalytic phase metal is selected from the groupconsisting of Fe, Cu, Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn, Sn, Ti, Ce, andmixtures thereof.

In another characterization of this composition that enhances baghouseunit performance, the composition further comprises an acid gas agent,the acid gas agent comprising a trivalent or higher Group 3 to Group 14metal-containing compound selected from the group consisting of acarbonate, an oxide, a hydroxide, an ionic salt precursor to a hydroxideand combinations thereof. In one example, the acid gas agent comprisesaluminum hydroxide.

In another characterization of this composition that enhances baghouseunit performance, the composition further comprises a flow aid, whereinthe flow aid is selected from the group consisting of graphite, talc,mica and combinations thereof. In one example, the flow aid comprisesgraphite.

In another characterization of this composition that enhances baghouseunit performance, the wt. % of the sorbent composition having a size ofless than 5 μm comprises not more than about 10 wt. % of the totalcomposition. In yet another characterization, the sorbent compositionfurther comprises a permeability additive, wherein the permeabilityadditive is selected from the group consisting of perlite, silica,diatomaceous earth, zeolites, and combinations thereof.

The foregoing embodiments of sorbent compositions may enhance baghouseunit performance by reducing the pressure drop across the baghousefilter, i.e., reduced pressure drop as compared to a composition thatconsists essentially of the sorbent. In one characterization, thepressure drop across the baghouse filter as measured in a permeabilitytest under an applied normal stress of 15 kPa at an air velocity of 0.5mm/s is not greater than about 85 mBar. In another characterization, thepressure drop across the baghouse filter as measured in a permeabilitytest under an applied normal stress of 15 kPa at an air velocity of 0.5mm/s is not greater than about 78 mBar. In another characterization, thepressure drop across the baghouse filter as measured in a permeabilitytest under an applied normal stress of 15 kPa at an air velocity of 0.5mm/s is not greater than about 65 mBar. In yet another characterization,the pressure drop across the baghouse filter as measured in apermeability test under an applied normal stress of 15 kPa at an airvelocity of 0.5 mm/s is not greater than about 50 mBar.

In certain characterizations, the foregoing embodiments of sorbentcompositions may enhance baghouse unit performance by reducing theheating of the composition as it resides on the baghouse filter. Onetechnique to measure the heating capability of a sorbent composition isto measure the specific enthalpy and/or the specific heat capacity ofthe sorbent composition, i.e., as compared to the specific enthalpy of acomposition that consists essentially of the sorbent. In one example,the specific enthalpy of the sorbent composition is at least about 10%less than a composition that consists essentially of the sorbent. Inanother characterization, the specific heat capacity of the sorbentcomposition at 160° C. is at least about 5% higher than a compositionthat consists essentially of the sorbent.

In one further characterization of the foregoing embodiments of asorbent composition, the specific enthalpy of the sorbent composition isat least about 10% less than a composition that consists essentially ofthe sorbent, the specific heat capacity of the sorbent composition at160° C. is at least about 10% higher than a composition that consistsessentially of the sorbent; and the pressure drop across a baghousefilter of the sorbent composition as measured in a permeability testunder an applied normal stress of 15 kPa at an air velocity of 0.5 mm/sis not greater than about 85 mBar.

In a further characterization of the foregoing embodiments of a sorbentcomposition, the specific enthalpy of the sorbent composition is atleast about 10% less than a composition that consists essentially of thesorbent, the specific heat capacity of the sorbent composition at 160°C. is at least about 10% higher than a composition that consistsessentially of the sorbent, and the pressure drop across a baghousefilter of the sorbent composition as measured in a permeability testunder an applied normal stress of 15 kPa at an air velocity of 0.5 mm/sis not greater than about 78 mBar.

In a further characterization of the foregoing embodiments of a sorbentcomposition, the specific enthalpy of the sorbent composition is atleast about 10% less than a composition that consists essentially of thesorbent, the specific heat capacity of the sorbent composition at 160°C. is at least about 10% higher than a composition that consistsessentially of the sorbent, and the pressure drop across a baghousefilter of the sorbent composition as measured in a permeability testunder an applied normal stress of 15 kPa at an air velocity of 0.5 mm/sis not greater than about 65 mBar.

In a further characterization of the foregoing embodiments of a sorbentcomposition, the specific enthalpy of the sorbent composition is atleast about 10% less than a composition that consists essentially of thesorbent, the specific heat capacity of the composition at 160° C. is atleast about 10% higher than a composition that consists essentially ofthe sorbent, and the pressure drop across a baghouse filter of thesorbent composition as measured in a permeability test under an appliednormal stress of 15 kPa at an air velocity of 0.5 mm/s is not greaterthan about 50 mBar.

In another embodiment of this disclosure, a method for making a sorbentcomposition having low self-heating properties is disclosed. The methodcomprises the steps of mixing a sorbent with at least a first heatmoderator to form the sorbent composition, wherein the first heatmoderator is selected from the group consisting of phyllosilicates,cyclosilicates, nesosilicates, colloidal silicates, aluminum silicates,mullite, perlite, organo-halogens, organo-phosphates, sodium sulfite,organic phosphinates, and combinations thereof, and wherein the sorbenthas a median particle diameter (D50) of not greater than about 30 μm.

A number of characterizations, refinements, enhancements and additionalfeatures are applicable to this embodiment of a sorbent composition thatenhances baghouse unit performance and comprises a surface agent. Thesecharacterizations, refinements, enhancements and additional features areapplicable to this embodiment of a sorbent composition individually orin any combination.

In one characterization, the first heat moderator comprises aphyllosilicate. In one example, the phyllosilicate is selected from thegroup consisting of kaolin, montmorillonite, illite, vermiculite,muscovite, kyanite, sillimanite, metakaolin, aluminum phyllosilicates,and combinations thereof. In one refinement, the phyllosilicatecomprises a montmorillonite. In another characterization of the methodfor making a sorbent composition having low self-heating properties, thefirst heat moderator comprises an aluminum silicate. In one refinement,the aluminum silicate is selected from the group consisting of zeolites,halloysite, andalusite, kyanite, sillimanite, kaolin, metakaolin,mullite, feldspar group minerals, and combinations thereof. In anotherrefinement, the aluminum silicate comprises halloysite. In yet anotherrefinement, the aluminum silicate comprises andalusite.

In another characterization of the method for making a sorbentcomposition having low self-heating properties, the first heat moderatorcomprises an aluminum phyllosilicate. In one refinement, the aluminumphyllosilicate comprises bentonite. In another characterization of themethod for making a sorbent composition having low self-heatingproperties, the first heat moderator comprises a nesosilicate. In yetanother characterization, the heat moderator comprises an organicphosphinate. In yet another characterization, the heat moderatorcomprises sodium sulfite.

In another characterization of the method for making a sorbentcomposition having low self-heating properties, a binding agent is firstcoated onto the sorbent, and the first heat moderator is coated onto thebinding agent. In one example, the binding agent comprises a polymerthat forms a charged species in water. In one refinement, the polymercomprises a polysaccharide. In yet a further refinement, thepolysaccharide comprises a compound selected from the group consistingof chitosan, dextran, cyclodextrin, and cellulose. In another example,the polymer is selected from the group consisting of polyethylenes,polyacrylates, and polyacrylamines. In one refinement, the polymer isselected from the group consisting of polyethyleneimine andpoly2(N,N-dimethyl amino) ethyl methacrylate. In one characterization,an additional layer of a binding agent is coated onto the first heatmoderator, and a second heat moderator is coated onto the additionallayer of the binding agent, and wherein the second heat moderator isselected from the group consisting of phyllosilicates, cyclosilicates,nesosilicates, colloidal silicates, aluminum silicates, mullite,perlite, organo-halogens, organo-phosphates, sodium sulfite, organicphosphinates, and combinations thereof, and wherein the first and secondheat moderators may be the same or different.

In another embodiment, a method for producing a sorbent compositionhaving low self-heating properties is disclosed. The method comprisesthe steps of: (a) coating a sorbent with a binding agent, wherein thebinding agent is selected from a group consisting of polymers that forma charged species in water, and wherein the sorbent has a medianparticle diameter (D50) of not greater than about 30 μm. The methodfurther comprises the step (b) of coating the binding agent with atleast a first heat moderator, wherein the heat moderator is selectedfrom a group consisting of phyllosilicates, cyclosilicates,nesosilicates, colloidal silicates, aluminum silicates, mullite,perlite, organo-halogens, organo-phosphates, sodium sulfite, organicphosphinates, and combinations thereof.

In one characterization of this method for producing a sorbentcomposition having low self-heating properties, the steps (a) and (b)are repeated at least two times, and the heat moderator may be the sameor different when steps (a) and (b) are repeated. In anothercharacterization, steps (a) and (b) are repeated at least two times, andthe heat moderator is different when steps (a) and (b) are repeated. Inanother characterization, steps (a) and (b) are repeated at least threetimes, and wherein the heat moderator may be the same or different whensteps (a) and (b) are repeated.

In another characterization, the binding agent comprises chitosan, andthe heat moderator comprises montmorillonite.

In another embodiment, a method for enhancing efficiency and safety of abaghouse unit is disclosed. The method comprises adding to a flue gasstream with an in-line baghouse unit, a sorbent composition, andcapturing the sorbent composition in the baghouse unit. The sorbentcomposition may be any of the sorbent compositions disclosed herein.

In one characterization, the method for enhancing the efficiency andsafety of a baghouse unit further comprises separately adding apermeability additive to the flue gas stream upstream from the baghouseunit. In another characterization, the permeability additive is selectedfrom the group consisting of diatomaceous earth, perlite, silica,silicates and combinations thereof.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a plant configuration and a method for the captureand sequestration of contaminants from a flue gas stream.

FIG. 2 illustrates a baghouse unit configuration and method ofparticulate matter capture.

FIG. 3 is a flow sheet illustrating a method for the manufacture of asorbent composition.

FIG. 4 illustrates specific enthalpy values for various sorbentcompositions.

FIG. 5 illustrates temperature of a sorbent composition of thisdisclosure (Sample F) versus a comparative sorbent composition (SampleA) measured in a Frank-Kamenetskii test cube at 240° C.

FIG. 6 illustrates the temperatures of a comparative prior art sorbentcomposition (Sample A) over time measured in a Frank-Kamenetskii testcube at 240° C.

FIG. 7 illustrates the temperatures of a sorbent composition of thepresent disclosure (Sample C) over time measured in a Frank-Kamenetskiitest cube at 260° C.

FIG. 8 illustrates the temperatures of a sorbent composition of thepresent disclosure (Sample F) over time measured in a Frank-Kamenetskiitest cube at 251° C.

FIG. 9 illustrates a thermal gravimetric analysis (TGA) of a comparativesorbent composition (Sample A) and a composition of the presentdisclosure (Sample G).

FIG. 10 illustrates the specific enthalpy of a prior art comparativesorbent composition (Sample A) and sorbent compositions of the presentdisclosure (Sample H and Sample I).

FIG. 11 illustrates the pressure drop in mBar across a powder bed asmeasured in a Permeability test over a range of applied normal stress of1 to 15 kPa of various sorbent compositions according to the presentdisclosure.

DETAILED DESCRIPTION

In many flue gas air pollution control trains a baghouse (BH) unit isused to remove the particulate matter including fly ash, dry sorbentinjection (DSI) material, PAC, and/or other conditioning agents from theflue gas stream prior to the flue gas stream exiting through the stack.Although ESP units generally require a lower capital cost than BH units,BH units often are more efficient and increase the contact time betweenthe sorbent (e.g., PAC) and the flue gases. Such increased contact timesare often necessary to adequately capture mercury from the flue gasstream. Further, TOXECON™ systems, which employ an ESP to capture flyash, and a subsequent BH to capture sorbents and control mercuryemissions, are popular because utilities don't need to factor incompatibility of the sorbent with respect to sale of fly ash to concretemanufacturers. TOXECON™ systems and methods are described in more detailin U.S. Pat. No. 6,451,094 by Chang et al. and U.S. Pat. No. 6,558,454by Chang et al., each of which is incorporated herein by reference inits entirety.

In one embodiment, a method for the treatment of the flue gas stream toremove mercury therefrom is provided. The method includes the step ofcontacting the flue gas stream with a sorbent composition, e.g., that isdisclosed herein, such as the method and flue gas train illustrated inFIG. 1. Coal, gas, and/or other energy product is combusted in a boiler101 producing a flue gas stream 102. As illustrated in FIG. 1, the fluegas stream 102 then proceeds through a set of pollution control deviceswhich may include an air heater unit 103 where the temperature of theflue gas stream 102 is reduced. Thereafter, the flue gas stream 102 maybe introduced to separation unit(s) which may include an electrostaticprecipitator (ESP) 104, a fabric filter or baghouse (BH) unit 105, orboth in sequence, such as for TOXECON™ systems as is illustrated FIG. 1.The BH unit 105 and/or ESP 104 along with the BH unit 105, removeparticulate matter from the flue gas, before exiting out a stack 106. Itwill be appreciated by those skilled in the art that the train mayinclude other devices not illustrated in FIG. 1, such as a selectivecatalytic reduction unit (SCR) and the like, and may have numerous otherconfigurations. In order to capture mercury from the flue gas 102, asorbent composition and other conditioning agents and/or dry sorbentinjection (DSI) agents may be introduced to (e.g., injected into) theflue gas stream 102 either before 107A or after 107B the air heater unit103, but before ESP separation unit 104 and/or the BH unit 105 whichwill remove the particulate DSI agents from the flue gas. Alternately,as with TOXECON™ systems, the DSI agents may be injected after 107C theESP 104 but before the BH unit 105.

FIG. 2 illustrates the configuration and operation of an example BH unit105. BH units are classified by cleaning method, and three types of BHunits predominate in the U.S.—reverse air (gas cleaning), pulse jet(compressed air cleaning) and shaker. Although different in someaspects, BH units have some common aspects that are illustrated in FIG.2. An inlet 201 serves as a conduit to receive a flue gas stream 102carrying particulate matter. Larger particulates 203, for example PAChaving a particle diameter of greater than about 10 μm, may loseentrainment and fall out of the gas stream into the hopper 204 when thevelocity of the stream is reduced. Finer particulates 205 (e.g., PAC,fly ash, dust, DSI particulates) that remain suspended in the stream aretrapped/captured by the suspended fabric filter bags 206 and continue tobe exposed to the flue gas 102 as the flue gas traverses the fabricfilter bags 206. Filtered flue gas exits through an outlet 207 that maylead to other treatment units or to the stack. Particulates 205collected on the fabric filter bags 206 are periodically removed fromthe filter surface via reverse air pulse or shaking such that theparticulates are collected by gravity in the hopper 204 and areperiodically transported out for disposal.

The BH unit illustrated in FIG. 2 is disclosed by way of example only,and the present disclosure encompasses the use of other types of BHunits, i.e., other types of particulate removal devices incorporatingfilter bags. Such BH units may include different cleaning mechanismssuch as reverse air, pulse jet and mechanical shaker. bar. See, forexample, U.S. Pat. No. 2,792,074 by Schlib et al., which is incorporatedherein by reference in its entirety.

There are several operational issues that may arise with respect to theuse of a BH unit 105. One potential issue, especially in TOXECON™systems, is that larger particulates 203, which may be predominatelyPAC, accumulate in the hopper 204 and pose a combustion threat.Combustion issues may arise due to adsorption of oxygen by the PACsorbent or other carbonaceous materials that accumulate in the hopper204, which releases heat (i.e., via the exothermic chemisorption ofoxygen). When large amounts of oxygen are adsorbed in a short amount oftime, the carbon can rapidly self-heat. The heat generated is difficultto dissipate because carbon inherently acts as an insulator, and thustemperatures can rise quickly, leading to dangerous conditions.

Sites that have BH units with such combustion issues may alter theirprocess conditions by cleaning the BH hopper 204 more frequently toavoid sorbent buildup. Also, some BH unit configurations include ahopper heater to keep the flue gas at a minimum temperature to avoidcondensation. In this instance, high temperatures may be mitigated byturning off the hopper heater. However, changing operating conditionsand procedures can be time consuming and expensive and requireadditional training. Further, turning off the hopper heater may increasecondensation. Additional issues arise if the flue gas is acidic since,at lower temperatures, the acidic flue gas may condense to form sulfuricacid and other liquids that can corrode plant equipment.

Another operational issue encountered with some BH units is that a cakelayer (i.e., a filter cake) forms on the filter bags 206 due todeposition of the particulates 205. Because it is advantageous to keepthe cake layer on the filter surface for enhanced mercury capture, andbecause cleaning of the filter accelerates filter wear, extending thecleaning cycle time (i.e., the time between cleanings of the fabricfilter) is desirable. However, PAC and other dust particles build up onthe filter bags 206 over time, eventually impeding the flow of airthrough the filter. In particular, PAC sorbents of reduced size, whichare increasingly popular due to their enhanced ability to capturemercury in flue gas streams, may decrease BH unit cleaning cycle timebecause the permeability of the filter cake is rapidly decreased by thepresence of such small particles in the filter cake, causing anundesirable pressure build-up. Further, DSI addition can also becounterproductive to BH function. Common DSI agents including trona,sodium bicarbonate, and hydrated lime react with the acid gas componentsof flue gas to form water, causing the filter cake to stick to thefilter bags.

It would be advantageous to provide sorbent compositions that overcomeone or more of the foregoing limitations of known sorbents (e.g., PAC),and that efficiently remove mercury from a flue gas stream, e.g., tomeet governmental regulations for mercury emissions. Such sorbentcompositions may exhibit improved permeability characteristics such thatcleaning cycle times in the BH unit may be increased. Such sorbentcompositions may ease the removal of the filter cake from the filterbag. Such sorbent compositions may exhibit reduced self-heatingcharacteristics to reduce the possibility of combustion. Any one or anycombination of the foregoing characteristics may be of benefit tomercury capture and/or to BH unit operations. In this regard, variousembodiments of sorbent compositions having one or more of increasedpermeability (e.g., in the filter cake), lower self-heating, and/orgreater resistance to water are provided in the present disclosure.

In one embodiment of the present disclosure, the sorbent compositionincludes a heat moderator that imparts low self-heating, e.g., reducedexothermic properties, as indicated by a reduced specific enthalpy, anincreased specific heat capacity, a decreased heat release upon exposureto an O₂ environment, and/or an increased auto-ignition temperature forthe sorbent composition, i.e., as compared to a sorbent composition thatconsists essentially of the sorbent. Carbon-based sorbents such as PACgenerate heat when oxygen is chemisorbed by the carbon, and if this heatis not dissipated, the temperature of the sorbent will increase,potentially to the point of uncontrolled self-heating. The heatmoderator may reduce the heating of the sorbent composition by absorbingheat, scavenging oxygen, creating air voids, and/or releasing water. Inone characterization, the heat moderator is selected from the groupconsisting of phyllosilicates, cyclosilicates, nesosilicates, colloidalsilicates, aluminum silicates, mullite, perlite, organo-halogens,organo-phosphates, sodium sulfite, organic phosphinates, andcombinations thereof. In one refinement, the heat moderator comprises aphyllosilicate, and examples of useful phyllosilicates include, but arenot limited to, kaolin, montmorillonite (e.g., natural or syntheticmontmorillonite), illite, vermiculite, muscovite, kyanite, sillimanite,metakaolin, aluminum phyllosilicates, and combinations thereof. Inanother refinement, the heat moderator comprises an aluminum silicate,and examples of useful aluminum silicates include, but are not limitedto, zeolites, halloysite, andalusite, kyanite, sillimanite, kaolin,metakaolin, mullite, feldspar group minerals, and combinations thereof.Among these, halloysite and andalusite may be particularly useful as aheat moderator. In another refinement, the heat moderator comprises analuminum phyllosilicate, and useful examples of aluminum phyllosilicatesinclude, but are not limited to, bentonite, or a nesosilicate. Inanother characterization the heat moderator may comprise an organicphosphate, an organic phosphinate and/or a sodium sulfite. Such organiccompounds may advantageously form a char when heated.

The heat moderator may be in particulate form, and may be admixed with aparticulate sorbent. In one characterization, the sorbent may be coatedand/or impregnated with one or more heat moderators to enhance thethermal properties of the sorbent compositions. For example, the heatmoderator may be coated onto the particulate sorbent as a solution(e.g., with dissolved components of the heat moderator) or as a slurry(e.g., with fine particulate solids of the heat moderator). The coatedheat moderator(s) may act as heat sinks or oxygen barriers for theunderlying sorbent In a particular example, the heat moderators coatedand/or impregnated onto the sorbent may include clays, such asmontmorillonite, bentonite, colloidal silica, or other compounds such asa tin alloy. Montmorillonite may be particularly useful as a heatmoderator.

These heat moderators may be used alone or in combination with oneanother. For example, the sorbent composition may comprise a particulatesorbent that is admixed with one or more particulate heat moderators,e.g., a second heat moderator, a third heat moderator, or even more. Inanother example, the sorbent composition comprises a first heatmoderator that is coated onto the sorbent and a second heat moderatorthat is coated onto the first heat moderator. In a further refinement, athird heat moderator is coated onto the second heat moderator. In yet afurther refinement, a fourth heat moderator coated onto the third heatmoderator.

In any event, the sorbent composition may comprise at least about 0.1wt. %, such as at least about 0.5 wt. % of a heat moderator to ensuresufficient heat moderation/dissipation in the sorbent composition.Further, it is believed that amounts of heat moderator greater thanabout 20 wt. % of the sorbent composition may not be of further benefitfor heat moderation and may begin to dilute the sorbent and decrease theability of the sorbent composition to otherwise function, e.g., tocapture mercury from the flue gas.

The sorbent composition may also include a binding agent to enhance thecohesiveness of the heat moderator on the sorbent, e.g., on aparticulate sorbent. That is, a binding agent may be applied to (e.g.,coated on) the particulate sorbent, with a heat moderator being coated(e.g., partially coated or fully coated) onto the binding agent. Thebinding agent may be a polymer, for example a polymer that readily formsions (i.e., charged anionic or cationic species) when dissolved inwater. Examples of such polymers include, but are not limited to,polysaccharides such as chitosan, dextran, cyclodextrin, and cellulose.Other examples include poly-L-lysine, polyamines, polyacrylates, andpolyacrylamide. Examples of these may be poly aminoester,polyethylenimine, and poly[2-(N,N-dimethylamino)ethyl methacrylate. Inone example, the binding agent is present in the sorbent composition ata concentration of at least about 0.05 wt. % and not greater than about10 wt. %.

The sorbent compositions disclosed herein may have reduced self-heatingor exothermal properties, e.g., as compared to the untreated particulatesorbent. These properties may include a reduced specific enthalpy (H),or total energy, in joules per gram (J/g), which is the total energy ofa thermodynamic system including internal energy and thermodynamicpotential. The specific enthalpy or energy change may be measured bydifferential scanning calorimetry (“DSC”) using a DSC instrument such asthe TA Instruments Q2000 differential scanning calorimeter (TAInstruments, New Castle, Del.) using heat flow measurements. Thespecific enthalpy may be calculated when heat is released by a materialundergoing a chemical reaction, for example upon oxidation. DSC may beused to detect the heat released after the environment changes frombeing inert (e.g., about 100% N₂) to 100% oxygen at a certaintemperature, here being 150° C. to 160° C. In a sorbent composition withreduced self-heating properties, the specific enthalpy should be lessnegative than the untreated sorbent such that less heat is released andtherefore less heat is stored in the sample.

Heat capacity is a measurable physical quantity, namely the ratio of theheat energy that is required to change the temperature of an object orbody to the total temperature change (ΔT) of the object or body, and isnormally reported in joule/degree Kelvin (K) or Celsius (C). Specificheat capacity (Cp), also known as specific heat, is the heat capacityper unit mass of material. Specific heat capacity may also be calculatedfrom the specific enthalpy measured by the DSC instrument. In a sorbentcomposition with decreased self-heating properties the specific heatcapacity should be increased, in that it takes more energy to raise thetemperature of a given mass of the sorbent composition. In onecharacterization, the specific heat capacity of the sorbent compositionat 160° C. is at least about 5% higher in joules per gram per ° C. (J/g° C.) than the specific heat capacity of the sorbent composition priorto addition of a heat moderator(s), e.g., a sorbent composition thatconsists essentially of the sorbent. In further refinements, thespecific heat capacity of the sorbent composition at 160° C. is at leastabout 10% higher, such as at least about 30% higher or even at leastabout 60% higher.

The heat moderators disclosed above may act as a heat sink or oxygenbarrier material, reducing specific enthalpy of the sorbent, andtherefore reducing self-heating potential. The effectiveness of a heatsink or oxygen barrier material, and therefore the reduced exothermalproperties of the sorbent compositions, can be determined by the amountof heat release. The sorbent compositions disclosed herein may havelower self-heating characteristics in that they will hold less heat, andtherefore the heat released and the specific enthalpy of the sorbentcomposition will be decreased.

In one characterization, the sorbent composition has a reduced specificenthalpy as compared to the sorbent without the addition of an additive.For example, in one embodiment the sorbent composition has a specificenthalpy that is at least about 10% less than the specific enthalpy of acomposition that consists essentially of the sorbent. In anotherembodiment, the specific enthalpy of the sorbent composition is at leastabout 15%, such as at least about 20%, or even at least about 25% lessthan a composition that consists essentially of sorbent, e.g., beforeaddition of a heat moderator.

Thermal gravimetric analysis (TGA) is a method of thermal analysis inwhich changes in the mass of materials are measured as a function oftemperature, e.g., at a constant heating rate. TGA can be used toevaluate the thermal stability of a material. In a desired temperaturerange, if a species is thermally stable, there will be substantially noobserved mass change. Negligible mass loss corresponds to little or noslope in the TGA trace. Here, the mass of a sorbent composition may bemeasured over time, with heating first to about 120° C. in the presenceof nitrogen (N₂) gas, then to about 150° C., followed by a change to a100% oxygen (O₂) environment. A change in weight of a sorbentcomposition upon heating to 120° C. is attributed to water release. Theamount of O₂ adsorbed by the material upon change to a 100% O₂environment is calculated. Amount of O₂ adsorbed correlates to thesusceptibility of the sorbent composition to be oxidized. Compositionsthat have an increased ability to be oxidized may have an increasedtendency to ignite at lower temperatures due to the exothermic nature ofoxidation.

Further, the sorbent compositions may have an increased auto-ignitiontemperature, which can be measured in a test based on theFrank-Kamenetskii theory. The Frank-Kamenetskii theory allows for thetemperature gradient of a mass or bulk of a substance to be taken intoaccount. If the material is a good thermal insulator, heat will betrapped inside even if there is a high surface area. The sorbentcompositions can be tested for heat build-up within a bulk sample byusing this test. For this test, a four inch cube is filled with a testsample and is placed in a heated environment such as an oven.Temperature is measured at different points within the cube being a topportion, middle, and bottom portion, as well the ambient temperaturesurrounding the cube. The temperature at which the sorbent compositionburns within a twenty-four hour period is described as the auto-ignitiontemperature. In one embodiment, sorbent compositions of the presentdisclosure have an auto-ignition temperature that is at least about 4%higher, or even 8% higher than a non-treated composition, e.g., than acomposition that consists essentially of the sorbent.

As is discussed above, another issue that may affect the efficiency of aBH unit is the rapid formation of a filter cake which decreases thepermeability of the flue gas through the filter. There are severalapproaches to mitigating filter cake permeability issues in accordancewith the present disclosure and these approaches may be implementedindividually or in combination to mitigate filter cake permeabilityissues. In one example, particulate sorbents of various sizes may bemixed in order to increase particle-particle void fraction and/ordecrease packing of particles. For instance a sorbent with relativelyhigher median particle diameter (D50), such as about 20 μm to 30 μm vs.about 8 μm to 14 μm, may be utilized with the smaller size sorbent tocreate a more permeable filter cake, reducing the pressure drop andtherefore allowing more air flow through the filters at similar orhigher loading of the sorbent composition in the filter. Consequently,as an example, mixing a batch of a first sorbent having a D50 of fromabout 20 μm to about 30 μm, such as about 25 μm, with a batch of asecond sorbent that has a D50 of not greater than about 20 μm, such asnot greater than about 15 μm, or even not greater than about 10 μm, mayoffer increased permeability but still offer some of the advantages ofthe increased mercury capture efficiency of smaller D50 PAC. As such, afirst sorbent, having a large D50 of between about 20 and 30 μm, may bemixed with a second sorbent having a smaller D50 of less than about 20μm, or even less than about 15 μm, in ratios such as about 5:1(large:small), or 4:1, or 3:1, or even 2:1, or 1:1. Described anotherway, the sorbent composition may have a multi-modal (e.g., bimodal)particle size distribution. In one characterization, the first mode ofthe bimodal size distribution may have a median particle diameter of atleast about 20 μm and not greater than about 30 μm. The second mode ofthe bimodal particle size distribution may have a median particlediameter of at least about 8 μm and not greater than 20 μm, where thefirst mode is larger than the second mode. For example, the differencein median particle diameter between the first mode and the second modemay be at least about 5 μm. The first and second sorbents may be thesame material, or may be comprised of different materials, and in oneembodiment the first and second sorbents are both PAC having similarporosity characteristics.

In a second example, the surface of the particles may be altered toreduce gas-particle friction or resistance between particles increasingpermeability and/or reducing pressure drop across the filter bydecreasing cohesion of the particles so that they slide more easilyagainst each other, against other particles, or against another surface.This may be achieved using a surface agent that either is coated onto oris admixed with the sorbent composition. Such a surface agent may reducefriction and may offer some additionally beneficial properties such astolerance to SO₃ while still maintaining functionality of oxidizing Hg⁰species to Hg⁺² species that are easier to capture. In an example, thesurface agent may be fluoropolymer with multiple carbon-fluorine bonds.The polymer may be coated onto the sorbent such as is described above ormixed with the sorbent with a high intensity mixer or used with thesorbent in a fluidized bed. The polymer may be a hydrophobic,aqueous-based polymer that may protect the sorbent from acids in theflue gas stream, such as SO₃. This may allow efficient mercury capturewhile also providing a sorbent composition that is less cohesive andshows a reduced pressure drop in a BH unit. Examples of suchfluoropolymers include, but are not limited to, polytetrafluoroethylene(PTFE), polyvinylfluoride (PVF), polyvinylidenefluoride (PVDF),polychlorotrifluoroethene (PCTFE), perfluoroalkoxy alkane (PFA),fluorinated ethylene propylene (FEP), ethylene tetrafluoroethylene(ETFE), ethylene chloro trifluoroethylene (ECTFE), fluorocarbon[chlorofluortrifluoroethylenevinylidenefluoride] (FPM/FKM),perfluoropolyether (PFPE), perfluorosulfonic acid (PFSA), orcombinations or derivatives thereof.

Yet another way to reduce pressure drop and/or increase permeability ofthe filter cake layer is through the addition of a permeability additiveto the sorbent composition. The permeability additives may be thosedisclosed as surface agents, or may comprise materials such asdiatomaceous earth, perlite (e.g., expanded perlite), silicas and/orsilicates, zeolite, or the like, that effectively increase the porosityof the filter cake. Such permeability additives may create air channelsin the filter cake that allow air flow through the cake, lengthening thetime between necessary cake filter cleanings, thereby decreasing downtime of the BH unit. Creation of air channels may also lead to enhancedheat dissipation through the filter cake. When utilized, the sorbentcomposition may include at least about 0.5 wt. % of the permeabilityadditive, and may include not greater than about 10 wt. % of thepermeability additive.

Any of the foregoing approaches to enhance permeability of the filtercake may be utilized, alone or in combination. The permeability of thesorbent compositions, i.e. that include a permeability additive orsurface agent, and/or have a multi-modal size distribution, may bemeasured in a permeability test, which measures the pressure drop acrossa powder bed. Pressure drop is a measure of the resistance to air flowbetween particles and through the filter cake (e.g., a powder bed). Thepressure drop according to the present disclosure, including the claims,is measured with the FT4 Powder Rheometer using a permeability testwhich measures the pressure drop across the powder bed as a function ofthe applied normal stress (kinematic) in kilopascal (kPa). The higherthe pressure drop that is measured, the more likely the powder is toinhibit flow through the baghouse. Typically, a powder with lowpermeability will generate a pressure drop of over 50 mbar from 2 kPa to15 kPa at an air velocity of 0.5 mm/s. In contrast, permeable powderswill register a much lower pressure drop under these conditions.

The example sorbent compositions disclosed herein that are formed tohave increased permeability may have a pressure drop as measured by theforegoing permeability test that is not greater than about 85 mBar underan applied normal stress of 15 kPa at an air velocity of 0.5 mm/s. Incertain characterizations, the pressure drop under these conditions isnot greater than about 78 mbar, such as not greater than about 65 mbar,such as not greater than about 50 mbar.

It will be appreciated that the sorbent compositions disclosed hereinmay be formulated to mitigate auto-ignition issues (e.g., to havedecreased specific heat capacity), to mitigate filter cake permeabilityissues, or may be formulated to mitigate both auto-ignition issues andfilter cake permeability issues. For example, the sorbent compositionmay include one or more heat moderators, either with or without abinding agent to enhance the adhesion of the heat moderator to thesorbent, and may also have mixed particle sizes to reduceparticle-particle packing efficiency, increase particle-particle voidspace, and reduce cohesion with other particles and surfaces in order toincrease permeability of the filter cake. In another embodiment, thesorbent composition is formulated to include one or more heat moderatorsand one or more surface agents to enhance permeability of the filtercake.

In one embodiment, a sorbent composition that enhances baghouse unitperformance is provided, wherein the composition has at least a bimodalparticle size distribution. In this embodiment, the sorbent compositionis a mixture of at least a first sorbent and a second sorbent, where thefirst sorbent has a median particle diameter of not greater than about30 μm and at least about 20 μm, and the second sorbent having a medianparticle diameter of not greater than about 20 μm and at least about 8μm, where the second sorbent has a median particle diameter that is lessthan the median particle diameter of the first sorbent. Althoughdescribed herein as comprising a first sorbent and a second sorbent, thefirst sorbent and the second sorbent may comprise substantially the samesorbent material, e.g., both the first and second sorbents may be PAC,where the two PACs have different particle size characteristics.

In one characterization, the difference in median particle diameterbetween the first mode and the second mode (e.g., between the first andsecond sorbent) is at least about 5 μm. In another aspect, the weightratio of the first sorbent to the second sorbent is not greater thanabout 5:1, such as not greater than about 4:1. In anothercharacterization, the weight ratio of the first sorbent to the secondsorbent is at least about 1:6, such as at least about 1:1, or even atleast about 2:1.

In addition to the foregoing, the sorbent compositions may include otheradditives, or be otherwise formulated, to enhance one or more propertiesof the sorbent composition that are not directly related to self-heatingand/or permeability of the sorbent composition. In one example, a solidparticulate flow aid may be admixed component with the sorbentcompositions. Alternately, it is envisioned that these flow aids couldbe coated onto the sorbent composition from a liquid slurry or solution,or otherwise associated with the sorbent composition to provide enhancedflow characteristics, e.g., during pneumatic transport of the sorbentcomposition. These flow aids may be compounds selected from the groupincluding silicates including phyllosilicates, minerals, graphite, andmixtures thereof. In one particular characterization, the flow aid maybe selected from the group consisting of mica, talc, graphite, andmixtures thereof, and in another particular characterization the flowaid is graphite. The sorbent composition may be characterized ascomprising not greater than about 10 wt. % of the flow aid, such ascomprising not greater than about 5 wt. % of the flow aid or evencomprising not greater than about 2 wt. % of the flow aid. Such flowaids are disclosed in more detail in commonly-owned U.S. patentapplication Ser. No. 14/145,731 by McMurray et al., which isincorporated herein by reference in its entirety. Other examples of flowaids include precipitated silica.

Further, a sorbent composition with a controlled particle sizedistribution may be employed to enhance the flow characteristics of thesorbent composition, e.g., during pneumatic transport. As such thesorbent composition may have reduced number of fine particles underabout 5 μm. Such sorbent compositions are disclosed in more detail incommonly-owned U.S. patent application Ser. No. 14/201,398 by McMurrayet al., which is incorporated herein by reference in its entirety. Inone characterization, the wt. % of the sorbent particles having a sizeof less than 5 μm comprises not greater than about 10 wt. % of the totalcomposition.

The sorbent composition also includes a sorbent (e.g., a particulatesorbent) that is selected to provide a large surface area for themercury oxidation and to sequester the oxidized mercury from the fluegas stream. In one aspect, the sorbent may include fixed carbon such asa porous carbonaceous material (e.g., powder activated carbon) having ahigh surface area and well-controlled pore structure. For example, thecarbonaceous material may be derived from coal, and in particular may bederived from lignite coal. In another characterization, the solidsorbent may comprise powdered activated carbon (PAC). The PAC may beformed from a variety of carbon sources such as wood, coconut shells andthe like. In one particular characterization, the sorbent comprises PACthat has been derived from coal, such as lignite coal. PAC derived fromcoal may have many advantageous morphological properties, such as highsurface area, high overall porosity and desirable pore sizecharacteristics that are advantageous for the sequestration of mercury.

The median average particle size (D50) of the particulate sorbent may berelatively small, particularly when the sorbent composition isengineered for the capture of mercury or other heavy metal contaminantsfrom a flue gas stream. In one characterization, the median averageparticle size of the solid sorbent is not greater than about 50 μm, suchas not greater than about 30 μm, or even not greater than about 25 μm.Particularly for the sequestration of mercury from a flue gas stream, itmay be desirable to utilize a solid sorbent having a median averageparticle size of not greater than about 20 μm, not greater than about 15μm and even not greater than about 12 μm. Characterized in another way,the median particle size may be at least about 5 μm, such as at leastabout 6 μm, or even at least about 8 μm. The D50 median average particlesize may be measured using techniques such as light scatteringtechniques (e.g., using a Saturn DigiSizer II, available fromMicromeritics Instrument Corporation, Norcross, Ga.).

In one characterization, the particulate sorbent (e.g., PAC) has arelatively high total pore volume and a well-controlled distribution ofpores, particularly among the mesopores (i.e., from 20 Å to 500 Å width)and the micropores (i.e., not greater than 20 Å width). Awell-controlled distribution of micropores and mesopores is desirablefor effective removal of mercury from the flue gas stream. While notwishing to be bound by any theory, it is believed that the mesopores arethe predominant structures for capture and transport of the oxidizedmercury species to the micropores, whereas micropores are thepredominate structures for sequestration of the oxidized mercuryspecies.

In this regard, the total pore volume of the solid sorbent (sum ofmicropore volume plus mesopore volume plus macropore volume) may be atleast about 0.10 cc/g, such as at least 0.20 cc/g, at least about 0.25cc/g or even at least about 0.30 cc/g. The micropore volume of thesorbent may be at least about 0.10 cc/g, such as at least about 0.15cc/g. Further, the mesopore volume of the sorbent may be at least about0.10 cc/g, such as at least about 0.15 cc/g. In one characterization,the ratio of micropore volume to mesopore volume may be at least about0.7, such as 0.9, and may be not greater than about 1.5. Such levels ofmicropore volume relative to mesopore volume may advantageously enableefficient capture and sequestration of oxidized mercury species by thesolid sorbent. Pore volumes may be measured using gas adsorptiontechniques (e.g., N₂ adsorption) using instruments such as a TriStar IISurface Area Analyzer 3020 or ASAP 2020 (Micromeritics InstrumentsCorporation, Norcross, Ga., USA).

In another characterization, the particulate sorbent has a relativelyhigh surface area. For example, the solid sorbent may have a surfacearea of at least about 350 m²/g, such as at least about 400 m²/g or evenat least about 500 m²/g. Surface area may be calculated using theBrunauer-Emmett-Teller (BET) theory that models the physical adsorptionof a monolayer of nitrogen gas molecules on a solid surface and servesas the basis for an analysis technique for the measurement of thespecific surface area of a material. BET surface area may be measuredusing the Micromeritics TriStar II 3020 or ASAP 2020 (MicromeriticsInstrument Corporation, Norcross, Ga.). The sorbent may alsoadvantageously include several different components that synergisticallymay decrease the time required for mercury oxidation and capture fromthe flue gas stream (e.g., enhance oxidation reaction kinetics and/ormass diffusional kinetics) and may advantageously reduce the totalamount of sorbent (e.g., powder activated carbon sorbent) that must beinjected into the flue gas stream to recover sufficient amounts ofmercury to meet applicable government regulations.

In this regard, the particulate sorbent may include minerals, e.g.,native minerals that originate from the coal source, such as lignitecoal. Such native minerals may enhance (e.g., catalyze) the oxidation ofelemental mercury by an oxidizing agent (e.g., an oxidizing agentcontained in the flue gas stream), an aqueous-based solubilizing mediumsuch as water to solubilize oxidized mercury and enhance massdiffusional kinetics, and a sorbent such as powder activated carbon(PAC) having a well-controlled pore size and pore size distribution toprovide a large surface area on which both kinetic mechanisms occur andto provide sufficient microporosity to sequester the oxidized mercury.The sorbent composition of matter may also have a relatively smallmedian particle diameter, i.e., as compared to typical sorbentcompositions used for injection into a flue gas stream.

Thus, one component of the particulate sorbent may include nativeminerals. The minerals may advantageously catalyze the oxidation of theelemental mercury in the flue gas stream. The presence of such mineralsmay thereby enhance the kinetics of the mercury oxidation such that areduced contact time with the flue gas stream is required to oxidize andremove sufficient amounts of mercury from the flue gas stream. As usedherein, these native minerals are a component of the sorbent, and aredifferent from the other components such as the heat moderator(s) thatare added to the sorbent to form the disclosed sorbent composition.

The mineral component of the sorbent may advantageously be comprised ofminerals including, but not limited to, aluminum-containing minerals,calcium-containing minerals, iron-containing minerals,silicon-containing minerals, silicate-containing minerals,sodium-containing minerals, potassium-containing minerals,zinc-containing minerals, tin-containing minerals, magnesium-containingminerals, and combinations thereof. These minerals may predominantly beoxide-based minerals, such as metal oxide minerals (e.g., CaO, Fe₂O₃,Fe₃O₄, FeO, Al₂O₃), and silicates (e.g. Al₂SiO₅). In onecharacterization, these minerals predominantly include metal oxides,particularly aluminum oxides and iron oxides. In anothercharacterization, the minerals include calcium-containing minerals,iron-containing minerals and aluminosilicates. These types of mineralsare particularly well adapted to catalyze the oxidation reaction of themercury. Iron-containing minerals are particularly well adapted tocatalyze the oxidation reaction, and in one characterization, theseminerals include at least 1 wt. % iron-containing minerals. The mineralsare intimately intertwined within the carbonaceous component of thesorbent within a well-controlled porous structure that facilitates theoxidation, capture and removal of mercury. To provide sufficientreaction activity and rapid oxidation kinetics, the particulate sorbentmay include at least about 20 weight percent of the minerals, such as atleast 25 weight percent and even at least about 30 weight percent of theminerals. However, excessive amounts of the minerals in the sorbent maybe detrimental to the capture of mercury. In this regard, the sorbentmay include not greater than about 50 weight percent of the minerals,such as not greater than about 45 weight percent. Advantageously, thesorbent may include not greater than about 40 weight percent of theminerals, such as not greater than about 35 weight percent of theminerals. The total mineral content of the sorbent may be measured by aTGA701 Thermalgravitmetric Analyzer (LECO Corporation, St. Joseph,Mich.). The specific types and amount of particular minerals may bemeasured by the Niton XL3t X-Ray Fluorescence (XRF) Analyzer (ThermoFisher Scientific Inc., Waltham, Mass.).

In addition, the sorbent may also include an amount of aqueous-basedsolubilizing medium such as water. The presence of a minimum level ofsolubilizing medium may advantageously enhance the mass diffusionalkinetics of the mercury oxidation and sequestration by solubilizingoxidized mercury species on the sorbent surface, e.g., within themespores and micropores. In this regard, the sorbent may include atleast about 2 weight percent of the solubilizing medium, such as atleast about 3 weight percent or at least about 6 weight percent.However, the amount of solubilizing medium in the sorbent should be notgreater than about 15 weight percent, such as not greater than about 12weight percent, or even not greater than about 10 weight percent toavoid interfering with the mercury oxidation reaction(s).

In addition to the sorbent and the other components disclosed above, thesorbent composition may also include catalytic metal, a precursor to acatalytic metal, a catalytic metal compound or a precursor to acatalytic metal compound. If the sorbent composition includes aprecursor to a metal or a precursor to a metal compound, the precursorshould be capable of rapidly converting to the catalytic metal or thecatalytic metal compound at the temperatures typically encountered in aflue gas stream, such as at least about 250° F. and not greater thanabout 700° F. The catalytic metal or catalytic metal compound may beassociated with the sorbent in that it may be covalently bound to thesorbent, surface bound, associated via ionic binding, and/orintramolecular forces.

The catalytic metal may be selected from metals that are categorized astransition metals, and may also include other metals including Fe, Cu,Mn, Pd, Au, Ag, Pt, Ir, V, Ni, Zn, Sn, Ti, Ce, and mixtures thereof. Inone characterization, the catalytic metal may be selected from Fe, Cu,Mn, Zn and combinations thereof. The catalytic metal(s) may be presentas elemental, or ionic species, or in the form of catalytic metalcompounds including oxides, hydroxides, or salts such as sulfates,carbonates, nitrates, and halides, of the metals. Examples of such metalcompounds may include, but not be limited to, copper (II) oxide (CuO),copper (II) chloride (CuCl₂), copper (II) nitrate (Cu(NO₃)₂), copper(II) hydroxide (Cu(OH)₂), or copper (II) carbonate (CuCO₃), iron (III)oxide (Fe₂O₃), iron (III) chloride (FeCl₃), iron (III) nitrate(Fe(NO₃)₃), iron (III) sulfate Fe₂(SO₄)₃, cerium (IV) oxide (CeO₂),manganese (IV) oxide (MnO₂), vanadium (V) oxide (V₂O₅), or zinc (II)oxide (ZnO). The use of such catalytic metals with the sorbentcomposition's is described in more detail in U.S. Patent App. No.62/005,304 by Huston et al., which is incorporated herein by referencein its entirety.

To further enhance the oxidation reaction kinetics and mass diffusionalkinetics, the sorbent composition may have a relatively small averageparticle size (e.g., median particle diameter, also known in the art asD50) particularly as compared to typical sorbent compositions used foractivated carbon injection. In this regard, the sorbent composition ofmatter may have a median particle diameter of not greater than about 30μm, such as not greater than about 20 μm, or even not greater than about15 μm, such as not greater than about 12 μm. The median particlediameter may be measured using techniques such as light scatteringtechniques (e.g., using a Saturn DigiSizer, available from MicromeriticsInstrument Corporation, Norcross, Ga.).

The sorbent composition may also be characterized by having awell-controlled particle density. Controlling the particle densitycorrelates to control over the surface area and total pore volume of thesorbent composition, which in turn affect mercury capture performance.

Particle density may be measured by liquid mercury volume displacement,in which case the result is referred to as the mercury particle density.In this regard, the sorbent composition may have a mercury particledensity of at least about 0.4 g/cc, such as at least about 0.6 g/cc.Conversely, the mercury particle density of the sorbent composition maybe not greater than about 0.9 g/cc, such as not greater than about 0.8g/cc. Particle density may be measured by the Micrometrics AutoPore IVMercury Porosimeter (Micromeritics Inc., Norcross, Ga., USA).

Particle density may also be measured by sedimentary volumedisplacement, in which case the result is referred to as the envelope orskeletal particle density. The envelope density refers to the weight ofsolid carbon per given volume occupied by a solid carbon. In thisregard, the envelope particle density of the sorbent composition may beat least about 0.4 g/cc, such as at least about 0.6 g/cc or at leastabout 0.7 g/cc. The envelope particle density of the sorbent compositionmay be not greater than about 1.0 g/cc, such as not greater than about0.9 g/cc, or even not greater than about 0.8 g/cc. Envelope particledensity may be measured using a Micromeritics GeoPyc Envelope DensityAnalyzer (Micrometrics, Inc., Norcross, Ga., USA).

The sorbent compositions may also include one or more oxidizing agentsthat may improve the adsorption of mercury from a flue gas stream.Oxidizing agents may include halogen salts such as inorganic halogensalts, which may include bromine compounds such as bromides, bromates orhypobromites, iodine compounds such as iodides, iodates or hypoiodites,or chlorine compounds such as chlorides, chlorates or hypochlorites. Theinorganic halogen salt may be an alkali metal compound or an alkalineearth metal compound, such as one containing a halogen salt, where theinorganic halogen salt is associated with an alkali metal such aslithium, sodium, and potassium or alkaline earth metal such asmagnesium, and calcium. Non-limiting examples of inorganic halogen saltsincluding alkali metal and alkaline earth metal counterions includecalcium hypochlorite, calcium hypobromite, calcium hypoiodite, calciumchloride, calcium bromide, calcium iodide, magnesium chloride, magnesiumbromide, magnesium iodide, sodium chloride, sodium bromide, sodiumiodide, potassium chloride, potassium bromide, potassium iodide, and thelike. The oxidizing agents may be included in the composition at anyconcentration, and in some embodiments, no oxidizing agent may beincluded in the compositions embodied by the present disclosure.

In some embodiments, the sorbent composition may include an acid gasagent such as, for example, an alkaline compound. Numerous alkalineagents are known in the art and currently used to remove sulfur oxidespecies from flue gas and any such alkaline agent may be used in theinvention. For example, in various embodiments, the alkaline additivemay be alkali oxides, alkaline earth oxides, hydroxides, carbonates,bicarbonates, phosphates, silicates, aluminates, and combinationsthereof, and in certain embodiments, the alkaline agent may be calciumcarbonate (CaCO₃), calcium oxide (CaO), calcium hydroxide (Ca(OH)₂);magnesium carbonate (MgCO₃); magnesium hydroxide (Mg(OH)₂) magnesiumoxide (MgO), sodium carbonate (Na₂CO₃), sodium bicarbonate (NaHCO₃),trisodium hydrogendicarbonate dihydrate (Na₃(CO₃)(HCO₃).2H₂O), andcombinations thereof.

In one particular example, the acid gas agent is a trivalent or higherGroup 3 to Group 14 metal-containing compound selected from the groupconsisting of a carbonate, an oxide, a hydroxide, an ionic saltprecursor to a hydroxide and combinations thereof. For example, thetrivalent or higher metal may be selected from Group 13 to Group 14metals, and in certain characterizations the trivalent or higher metalis a Group 13 metal. For example, the trivalent or higher metal may bealuminum. In other characterizations, the trivalent or higher metal maybe tin. The metal-containing compound may comprise an anion and acation, where the cation includes the trivalent or higher metal. Themetal-containing compound may also be a metal oxide, for example SnO₂.The metal-containing compound may also be a metal hydroxide, such asaluminum hydroxide. The metal-containing compound may also be an ionicsalt precursor to a metal hydroxide, such as an ionic salt that includesa polyatomic anion where the trivalent or higher Group 3 to Group 14metal is a component of the polyatomic anion. The polyatomic anion maybe an oxoanion and the metal may be aluminum. For example, the ionicsalt may be sodium aluminate or sodium stannate. Such acid gas agentsare disclosed in more detail in commonly-owned U.S. patent applicationSer. No. 14/142,636 by Wong et al., which is incorporated herein byreference in its entirety.

FIG. 3 is a flow sheet that illustrates an exemplary method for themanufacture of a sorbent composition in accordance with one embodiment.The manufacturing process begins with a carbonaceous feedstock 301 suchas low-rank lignite coal with a relatively high content of naturaldeposits of native minerals. In the manufacturing process, the feedstockis subjected to an elevated temperature and one or more oxidizing gasesunder exothermic conditions for a period of time to sufficientlyincrease surface area, create porosity, alter surface chemistry, andexpose and exfoliate native minerals previously contained withinfeedstock. The specific steps in the process include: (1) dehydration302, where the feedstock is heated to remove the free and bound water,typically occurring at temperatures ranging from 100° C. to 150° C.; (2)devolatilization 303, where free and weakly bound volatile organicconstituents are removed, typically occurring at temperatures above 150°C.; (3) carbonization 304, where non-carbon elements continue to beremoved and elemental carbon is concentrated and transformed into randomamorphous structures, typically occurring at temperatures of from about350° C. to about 800° C.; and (4) activation 305, where steam, air orother oxidizing agent(s) are added and pores are developed, typicallyoccurring at temperatures above 800° C. The manufacturing process may becarried out, for example, in a multi-hearth or rotary furnace. Themanufacturing process is not discrete and steps can overlap and usevarious temperatures, gases and residence times within the ranges ofeach step to promote desired surface chemistry and physicalcharacteristics of the manufactured product.

After activation 305, the product may be subjected to a comminution step306 to reduce the particle size (e.g., reduce the median particlediameter) of the activated product. Comminution 306 may occur, forexample, in a mill such as a roll mill, jet mill or other like process.Comminution 306 may be carried out for a time sufficient to reduce themedian particle diameter of the thermally treated product to not greaterthan about 25 μm. In one embodiment, an additive being a heat moderator,a surface agent, or a permeability additive may be alternatively admixedwith the product before 306A or after 306B comminution 306. In anotherembodiment, a slurry or aqueous mixture or solution of an additive beinga heat moderator, permeability additive, or surface agent may bealternatively sprayed on or mixed with the product either before 306A orafter 306B comminution to coat the sorbent.

In yet another embodiment, an aqueous mixture or solution of additivemay be sprayed or coated on the product after comminution 306B and driedto create a mono-layer coated product. This mono-layer may be comprisedof a binding agent that binds the heat moderator to the sorbent, as isdescribed above. Following coating of the heat moderator onto thebinding agent layer, a second layer of binding agent and heat moderatormay be sprayed or coated onto the now bi-layer coated product and driedto create the bi-layer coated product. These coating and drying stepsmay be repeated multiple times to create multiple bi-layers on theproduct. The heat moderators that are used for each layer may be theselected from groups as previously described and may be the same in eachlayer or may differ in each layer.

In the event that manufacturing conditions result in a differentparticle size distribution than is desired, classification 307 may becarried out to separate particles by size. For example, classification307 may be carried out using an air classifier, screen/meshclassification (e.g., vibrating screens), sieves, or centrifugation.Sorbents that have a higher median particle diameter, of for instance aD50 of 20 μm to 30 μm, may be mixed with a sorbent having a smallermedian particle diameter, such as a D50 of 15 μm, or even 12 μm, or even10 μm or less, at various ratios to obtain a product with desirablecharacteristics such as increased permeability or mercury captureperformance, e.g., through the use of a bimodal particle sizedistribution. Further additives may be admixed, coated or impregnated oncompositions that have been classified, and/or classified and mixed topredetermined ratios.

EXAMPLES Example 1

Several example sorbent compositions according to the present disclosureare prepared and are tested to measure the thermal properties ascompared to a prior art sorbent composition. These properties arecompared to Sample A, which is a prior art PAC sorbent composition,namely PowerPAC Premium®, available from ADA Carbon Solutions,Littleton, Colo. Sample A is a particulate PAC-based sorbent that isbrominated and has a particle size such that a minimum of 95% of thesorbent is −325 mesh. Example sorbent compositions, Samples C-G, aremade by mixing the sorbent of Sample A with a 10 wt. % concentration ofa heat moderator in a ball milling device. Prior to mixing with SampleA, the heat moderator is milled into particles having a D50 particlediameter of about 5 μm or less. Table I lists the heat moderators forSamples C-H. Natural montmorillonite (Nanofil® 116) is obtained fromSouthern Clay Products, Inc., Gonzales, Tex. The halloysite clayadditives (DRAGONITE HP™ and DRAGONITE XR™) are obtained from AppliedMinerals, Inc., New York, N.Y. The organic phosphinate additive is basedon aluminum diethyl-phosphinate (Exolit® OP 1230) from ClariantInternational Ltd., Muttenz, Switzerland, and the sodium sulfiteadditive is obtained from Sigma Aldrich, St. Louis, Mo.

Differential scanning calorimetry (“DSC”) is used to detect the heatflow, specifically to quantitatively detect the exothermal peak afterthe chamber atmosphere is switched from an inert (N₂) atmosphere to a100% oxygen atmosphere at a certain temperature. The effectiveness ofthe heat moderators can be determined by the amount of heat releasedafter this change in atmosphere. The DSC instrument is a TA InstrumentsQ2000 differential scanning calorimeter available from TA Instruments,New Castle, Del. For these tests, a sample of the sorbent composition isplaced in a sealed chamber and is heated to and stabilized at 150° C.The atmosphere is then switched from 100% N₂ to 100% O₂ and the chambertemperature is increased to 160° C. A release of heat from the sorbentcomposition is observed due to the rapid oxygen adsorption by the PAC.The heat released by this exothermic reaction is measured over time asheat flow in joules (J) and the specific enthalpy of the sorbentcomposition in joules per gram (J/g) may be calculated

Such DSC measurements are made for Comparative Sample A and Samples C-Gand the specific enthalpy in joules per gram (J/g) for each sample isillustrated in FIG. 4. Further, specific heat capacity is calculatedfrom the collected data and these values as well as the specificenthalpy, percent reduction in specific enthalpy as compared to SampleA, and percent increase in specific heat capacity as compared to SampleA, are reported in Table I. Example compositions that include heatmoderators demonstrate specific enthalpy reductions of as much as 15%,and specific heat capacity increase by as much as 61% as is indicated inTable I, reflecting lowered reactivity with the oxygen and thus reducedself-heating properties.

TABLE I Sorbent Compositions Specific Enthalpy and Heat Flow andCapacity % Specific % Specific Specific Enthalpy Heat Heat En- ReductionCapacity Capacity Additive thalpy from at 160° C. Increase Sample (10wt. %) (J/g) Baseline (J/g ° C.) at 160° C. A None −3.9 Baseline 1.03Baseline C natural −3.7  5% 1.37 33 montmorillonite (Nanofil ® 116) Dhalloysite clay −3.5 10% 1.38 34 (Dragonite- HP ™) E halloysite clay−3.3 15% 1.13 10 (Dragonite- XR ™) F Organic −3.3 15% 1.66 61phosphinate (Exolit ® OP 1230) G sodium sulfite −3.4 13% 1.42 38

Example 2

To better understand how a sorbent composition sample may perform in asetting that more closely mimics the BH unit conditions, a bulk lot ofeach example composition is tested in what is known as theFrank-Kamenetskii theory test. The Frank-Kamenetskii theory allows forthe temperature gradient of a mass or bulk of a substance to be takeninto account. If the material is a good thermal insulator, heat will betrapped within the sample even if there is a high surface area. Theexample compositions can be tested for heat build-up within a bulksample by a method wherein a four inch cube is filled with a test sampleand temperature is measured at different points within the cube, namelya top, middle, and bottom portion along with the ambient temperaturesurrounding the cube, in a heated environment such as an oven.

FIG. 5 illustrates ambient temperature readings in the middle of thecube during heating at a constant temperature of 240° C. of thecomparative Sample A and Sample E during a Frank-Kamenetskii test usinga 4-inch carbon steel cubic container. During this test, the oventemperature is kept stationary and the temperature of the samples ismeasured over time. 240° C. is previously determined to be theauto-ignition temperature for comparative Sample A by testing over arange of temperatures, and FIG. 6 illustrates that Sample A auto-igniteswithin about 6 hours at 240° C. The addition of the halloysite heatmoderator (Dragonite-XR™) in Sample E prevents the sample from ignitingat the baseline test temperature of 240° C., i.e., the auto-ignitiontemperature of the sample sorbent composition has been increased throughthe addition of the halloysite heat moderator.

FIGS. 6-8 illustrate temperature readings of the comparative Sample A,Sample C, and Sample E, respectively, in the oven, at the top, in themiddle, and at the bottom of the samples during this Frank-Kamenetskiitest. FIG. 6 illustrates readings for the comparative Sample A with aconstant oven temperature at the auto-ignition temperature of the sample(240° C.). At about 6 hours, the temperature in the middle and top ofthe cube increase dramatically, indicating auto-ignition. Samples C andE are determined to exhibit higher auto-ignition temperatures of 260° C.and 251° C., respectively. FIG. 7 illustrates temperature readings forSample C, in the oven, at the top of the sample, in the middle, and atthe bottom of the sample. Sample C exhibits increased auto-ignitiontemperature. FIG. 8 illustrates temperature readings for Sample E, inthe oven, at the top of the sample, in the middle, and at the bottom ofthe sample, illustrating increased auto-ignition temperature. Table IIshows results of the tests over a range of temperatures to determine theauto-ignition temperature.

TABLE II Auto-ignition Sample Temp (° C.) A 240 C 260 E 251

Example 3

Thermal gravimetric analysis (TGA) is a method of thermal analysis inwhich changes in physical and/or chemical properties of materials aremeasured as a function of increasing temperature with a constant heatingrate. TGA can be used to evaluate the thermal stability of a material.In a desired temperature range, if a species is thermally stable, therewill be no observed mass change. Negligible mass loss corresponds tolittle or no slope in the TGA trace. Here, weight of the sample ismeasured over time, with heating first to 120° C. in the presence ofnitrogen (N₂) gas, then to 150° C., followed by a change to a 100%oxygen (O₂) environment. A change in weight of a sorbent compositionupon heating to 120° C. is attributed to water release. The amount of O₂adsorbed by the composition may be calculated from the gain in mass whenthe composition is exposed to the 100% O₂ environment at 150° C. In FIG.9, a thermal gravimetric analysis of the comparative Sample A and SampleF is illustrated. The weight, of each sample, in percent, is plottedagainst time. Sample A absorbs 0.03% O₂, whereas Sample F only absorbs0.01% O₂, indicating a 67% reduction in the amount of O₂ absorption bySample F. Reduced O₂ absorption indicates reduced combustibility ofSample F.

Example 4

Comparative Sample A is treated with a binding agent, chitosan, andnatural or synthetic montmorillonite, to create bilayers. Threebi-layers of chitosan-montmorillonite are coated onto Sample A to makeSample H and Sample I in the following manner. First, Sample A isdispersed in 0.1 wt. % chitosan solution, the mixture is magneticallystirred for 10 minutes, filtered, and dried in a convection oven at 80°C. Next the dried composition is dispersed in a 0.3 wt. %montmorillonite dispersion, magnetically stirred for 10 minutes,filtered, and dried in the same oven at 80° C. These two steps arerepeated two additional times to create a triplechitosan-montmorillonite bi-layer on Sample A. For Sample H, a naturalmontmorillonite (Nanofil® 116) is used for the heat moderator coating.For Sample I a synthetic montmorillonite (Laponite®) is used for theheat moderator coating. FIG. 10 illustrates the heat release during thedifferential scanning calorimetry test described previously attemperatures between 150° C. and 160° C. Table III summarizes results ofthis test. The chitosan-natural montmorillonite triple bi-layer coatingreduces specific enthalpy by 26% and the chitosan-syntheticmontmorillonite triple bi-layer coating synthetic reduces specificenthalpy by 54%.

TABLE III Differential Scanning Calorimetry Results from Bi-layer CoatedSamples Specific Enthalpy % Enthalpy Sample Additive (J/g) Reduction ANone −3.9 Baseline H chitosan & natural −2.9 26% montmorillonite triplebi-layer coating I chitosan & synthetic −1.8 54% montmorillonite triplebi-layer coating

Example 5

To evaluate how sorbent compositions might behave in a BH unit withregard to exhaust flow and/or impedance of the exhaust flow through theBH unit permeability tests are performed as described above. Two sorbentcompositions are used for comparison including a smaller median particlediameter sample, Sample K, being FastPAC Premium® (ADA CarbonSolutions), with a D50 of about 12 μm, and a larger median particlediameter sample, Sample R, being PowerPAC Premium® PLUS (ADA CarbonSolutions), with a D50 of about 20 μm.

FIG. 11 illustrates permeability tests of example sorbent compositions,being mixtures of Sample K and Sample R in given ratios, with or withoutan admixed flow agent additive, the additive being graphite (Micro 850grade, Asbury Carbons, Asbury Graphite Mill, Inc., Asbury, N.J.). Thistest, illustrated in FIG. 11, measures pressure drop as a function ofapplied normal stress. In the test the air velocity is held constant at0.4 mm/s and the applied normal stress is increased to 15 kPa. Thepressure drop is measured at 15 kPa and these results are summarized inTable IV.

TABLE IV Pressure Drop of Example Sorbent Compositions Pressure %Improvement Composition Drop compared to Sample (% small-% large) (mBar)Sample K K* 100% K 84.5 — (12 μm) L K + 78.5  8 1 wt. % Graphite M 50%K + 50% R 64.4 25 N 25% K + 75% R 55.9 34 O 25% K + 75% R + 53.0 36 1wt. % Graphite P 15% K + 85% R 48.3 44 Q 15% K + 85% R + 45.2 47 1 wt. %Graphite R* 100% R 50.1 N/A (20 μm) *comparative example

Mixing the smaller median particle diameter Sample K with the largermedian particle diameter Sample R decreases the pressure drop comparedto pure Sample K, indicating increased permeability of the mixedsamples. The addition of 1 wt. % graphite to the sorbent compositionfurther decreases pressure drop. Example compositions show improvedpermeability as shown with a decreased pressure drop by as much as 47%by over the small median particle diameter PAC, Sample K at an appliednormal stress of 15 kPa.

While various embodiments have been described in detail, it is apparentthat modifications and adaptations of those embodiments will occur tothose skilled in the art. However, is to be expressly understood thatsuch modifications and adaptations are within the spirit and scope ofthe present disclosure.

1-45. (canceled)
 46. The composition of claim 123, wherein thecomposition comprises a permeability additive.
 47. The composition ofclaim 46, wherein the permeability additive is selected from the groupconsisting of perlite, silica, diatomaceous earth, zeolite andcombinations thereof. 48-65. (canceled)
 66. The composition of claim123, the composition comprising: a first particulate sorbent having amedian particle diameter of not greater than about 30 μm and at leastabout 20 μm; and a second particulate sorbent having a median particlediameter of not greater than about 20 μm and at least about 8 μm,wherein the median particle diameter of the second sorbent is less thanthe median particle diameter of the first sorbent.
 67. The compositionof claim 66, wherein the first particulate sorbent and the secondparticulate sorbent comprise substantially the same sorbent material.68. The composition of claim 66, wherein the difference in medianparticle diameter between the first particulate sorbent and the secondparticulate sorbent is at least about 5 μm.
 69. The composition of claim68, wherein the weight ratio of the first particulate sorbent to thesecond particulate sorbent is not greater than about 5:1.
 70. Thecomposition of claim 68, wherein the weight ratio of the firstparticulate sorbent to the second particulate sorbent is not greaterthan about 4:1.
 71. The composition of claim 68, wherein the weightratio of the first particulate sorbent to the second particulate sorbentis at least about 1:6.
 72. The composition of claim 68, wherein theweight ratio of the first particulate sorbent to the second particulatesorbent is at least about 1:1
 73. The composition of claim 68, whereinthe weight ratio of the first particulate sorbent to the secondparticulate sorbent is at least about 2:1.
 74. The composition of claim66, further comprising an oxidizing agent.
 75. The composition of claim74, wherein the oxidizing agent comprises an inorganic halogen salt.76-80. (canceled)
 81. The composition of claim 66, further comprising aflow aid selected from the group consisting of graphite, talc, mica andcombinations thereof.
 82. (canceled)
 83. The composition of claim 66,wherein the sorbent composition comprises not more than about 10 wt. %sorbent particles having a size of less than 5 μm based on the totalsorbent composition.
 84. The composition of claim 66, further comprisinga permeability additive selected from the group consisting of perlite,silica, diatomaceous earth, zeolites, and combinations thereof. 85.(canceled)
 86. (canceled)
 87. The composition of claim 123, wherein thepressure drop as measured in a permeability test under an applied normalstress of 15 kPa at an air velocity of 0.5 mm/s is not greater thanabout 65 mBar.
 88. The composition of claim 123, wherein the pressuredrop as measured in a permeability test under an applied normal stressof 15 kPa at an air velocity of 0.5 mm/s is not greater than about 50mBar. 89-122. (canceled)
 123. A sorbent composition that enhancesbaghouse unit performance comprising a particulate sorbent having amedian particle diameter (D50) of not greater than about 30 μm, andwherein a pressure drop as measured in a permeability test under anapplied normal stress of 15 kPa at an air velocity of 0.5 mm/s is notgreater than about 78 mBar.
 124. The composition of claim 46, whereinthe composition comprises at least about 0.5 wt. % of the permeabilityadditive.
 125. The composition of claim 46, wherein the compositioncomprises not greater than about 10 wt. % of the permeability additive.126. The composition of claim 46, further comprising an oxidizing agent.127. The composition of claim 126, wherein the oxidizing agent comprisesan inorganic halogen salt.